Method for manufacturing a thin film recording head

ABSTRACT

The invention provides a method of forming a thin film recording head including an upper magnetic substance, a lower magnetic substance cooperating with the upper magnetic substance to form a magnetic circuit, at least one coil layer interposed between the upper and lower magnetic substances, the coil layer being configured in a coil pattern, and an insulative layer interposed between the upper and lower magnetic substances and surrounding the coil pattern. The insulative layer is composed of hard-cured photoresist. A peak intensity ratio of a surface portion of the insulative layer is equal to or less than 0.5 relative to a peak intensity of aromatic C═C bonding, which aromatic is a main constituent of the photoresist. The peak intensity ratio represents an amount of hydrophilic radical. The invention suppresses the hydrophilic property of a hard-cured photoresist layer to thereby provide an advantage of enhancement of electrical insulation and reduction of noises of a thin film head.

This is a divisional of Application Ser. No. 08/363,314 filed Dec. 23,1994, now U.S. Pat. No. 5,659,450 issued Aug. 19, 1997.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a thin film recording head for use with amagnetic recording device such as a magnetic disk, and also to a methodfor manufacturing such a thin film.

2. Description of the Related Art

FIG. 1 is a cross-sectional view illustrating a prior thin film head.The prior thin film is manufactured generally as follows. First, on anAl₂ O₃ -TiC substrate 1 is formed an insulative layer 2 composed ofalumina by means of sputtering. Then, on the insulative layer 2 isformed a lower magnetic layer 3 by sputtering or plating soft magneticsubstance such as a permalloy. On the lower magnetic layer 3 is thenformed an insulative gap layer 4 composed of alumina and having apredetermined thickness. Then, an unnecessary rear portion of theinsulative gap layer 4 is removed by etching. Then, photoresist isapplied on the insulative gap layer 4 by a spin-coating process in orderto eliminate an irregularity due to the lower magnetic layer 3. Then, aresultant is subject to heat treatment at approximately 250 degreescentigrade to thereby form a hard-cured photoresist layer 5a.

Then, on the hard-cured photoresist layer 5a is formed a first layerwhich is to act as a layer for preventing the photoresist layer 5a frompeeling off, and on the first layer is formed a second layer which is toact as an underlying layer for plating. The first and second layers areformed by means of sputtering. Then, a coil layer is patterned on thesecond layer with photoresist, and then coils 6 are formed by means ofplating. Then, the photoresist having been used for coil patterning isremoved, and further unnecessary portions of the first and second layersare removed by ion-milling. In order to smooth irregularities formed bythe coils 6, photoresist is applied over the coils 6, and then subjectto a heat treatment at 250 degrees centigrade. Thus, there is formed ahard-cured photoresist layer 5b. Then, on the insulative hard-curedphotoresist layer 5b is formed an upper magnetic layer 7 in a similarway as that of the lower magnetic layer 3. Thus, a transducer portion ofa thin film recording head is completed. The hard-cured photoresistlayer 5b provides many advantages. For instance, the hard-curedphotoresist layer 5b eliminates irregularities formed by the coils 6,enhances electrical insulation, and smoothes a shoulder portionindicated with C and C'.

Recently, with down-sizing of a device and high densification ofmagnetic recording, a space between a head and a medium has been muchreduced. As a result, it is required to apply a certain plus voltage(for instance, +6 V) to a coil for operating a transistor-drivercircuit. However, it has been found that if a prior thin film head wouldbe used for applying a certain voltage to a coil, there occursdielectric breakdown of a head and an output voltage of a head isdecreased to thereby produce a larger noise.

SUMMARY OF THE INVENTION

In view of the foregoing problem of the prior thin film recording head,it is an object of the present invention to provide a thin filmrecording head which does not induce dielectric breakdown which would beinduced by use of the above mentioned prior thin film heads and whichhas superior output characteristics suitable for highly densifiedmagnetic recording.

Another object of the invention is to provide a method for manufacturingthe above mentioned thin film recording head.

In one aspect, the invention provides a thin film recording headincluding an upper magnetic substance, a lower magnetic substancecooperating with the upper magnetic substance to form a magneticcircuit, at least one coil layer interposed between the upper and lowermagnetic substances, the coil layer being configured in a coil pattern,and an insulative layer interposed between the upper and lower magneticsubstances and surrounding the coil pattern. The insulative layer iscomposed of hard-cured photoresist. A peak intensity ratio of a surfaceportion of the insulative layer is equal to or less than 0.5 relative toa peak intensity of aromatic C═C bonding, which aromatic is a mainconstituent of the photoresist. The peak intensity ratio represents anamount of hydrophilic radical.

In a preferred embodiment, the surface portion of the insulative layerincludes a portion located lower than the coil layer and between coilsforming the coil pattern.

In another preferred embodiment, the hydrophilic radical is carbonylgroup.

In still another preferred embodiment, the surface portion of theinsulative layer has a higher cross-linking density than that of aninsulative layer located under the coil layer.

In yet another preferred embodiment, the surface portion of theinsulative layer has a higher cross-linking density than that of aninsulative layer located under the coil layer by at least 10%.

In still yet another preferred embodiment, the surface portion of theinsulative layer is densified in terms of cross-linking by implantingion of an impurity thereinto.

In further preferred embodiment, the impurity is selected fromimpurities having a small diffusion coefficient in thermosettingphotoresist.

In further preferred embodiment, the impurities include P, As, B, Si andSn.

In further preferred embodiment, the ion is implanted at an amount ofdopant in the range of 10¹⁴ to 10¹⁵ cm⁻².

The invention also provides a thin film recording head including anupper magnetic substance, a lower magnetic substance cooperating withthe upper magnetic substance to form a magnetic circuit, at least onecoil layer interposed between the upper and lower magnetic substances,the coil layer being configured in a coil pattern, and an insulativelayer interposed between the upper and lower magnetic substances andsurrounding the coil pattern. The insulative layer is composed ofhard-cured photoresist. A surface portion of the insulative layer has ahigher cross-linking density than that of an insulative layer locatedunder the coil layer by at least 10%. The surface portion of theinsulative layer comprises a portion located lower than the coil layerand between coils forming the coil pattern.

In another aspect, the invention provides a method for manufacturing athin film recording head, including the steps of forming a firsthard-cured photoresist layer on a lower magnetic substance, forming anunderlying layer for plating on the first hard-cured photoresist layer,forming a coil layer on the underlying layer, the coil layer beingconfigured in a coil pattern, forming a second hard-cured photoresistlayer over the coil pattern, forming an upper magnetic substance on thesecond hard-cured photoresist layer, and removing unnecessary portionsof the underlying layer by ion-milling in Ar atmosphere with anacceleration voltage of ion-milling being equal to or less than 500 V.

In a preferred embodiment, the underlying layer is composed of Cu.

The invention also provides a method for manufacturing a thin filmrecording head, including the steps of forming a first hard-curedphotoresist layer on a lower magnetic substance, forming an underlyinglayer for plating on the first hard-cured photoresist layer, forming acoil layer on the underlying layer, the coil layer being configured in acoil pattern, forming a second hard-cured photoresist layer over thecoil pattern, forming an upper magnetic substance on the secondhard-cured photoresist layer, and implanting ion of an impurity at anamount of dopant in the range of 10¹⁴ to 10¹⁵ cm⁻² into a portion of thesecond hard-cured photoresist layer located lower than the coil layerand between coils forming the coil pattern.

In a preferred embodiment, the impurity is selected from impuritieshaving a small diffusion coefficient in thermosetting photoresist.

In another preferred embodiment, the impurities include P, As, B, Si andSn.

The inventor has found that the deterioration of electrical insulationof a hard-cured photoresist layer located between coils inducesdielectric break down of a head and decrease of an output voltage of ahead to thereby produce a larger noises

The deterioration of electrical insulation is considered as follows.FIG. 1 shows the results of the experiment, showing a relationshipbetween a leak current and a peak intensity ratio of a carbonyl group,which is one of hydrophilic groups, relative to the C═C peak intensityof novolak resin which is a main constituent of photoresist. As shown inFIG. 2, with the increase of an amount of hydrophilic carbonyl groups ina surface portion of a hard-cured photoresist layer, which portion islocated under a coil layer and further between adjacent coils comprisinga coil pattern, the hard-cured photoresist tends to absorb humidity andhence decrease its electrical insulation. Such a decrease of theelectrical insulation has been found when there were also present otherhydrophilic groups such as acid anhydride and aromatic ketone group. Ithas been confirmed by the results of the experiment that, supposing thata threshold value of a leak current is to be determined to be 10⁻⁶ A,the characteristics of a thin film recording head are not affected if apeak intensity ratio of all peaks of hydrophilic groups such as carbonylgroup, acid anhydride and ketone group is equal to or less than 0.5.

On the other hand, FIG. 4 shows the results of the experiment, showing arelationship between a carbonyl peak intensity ratio and ion-millingacceleration voltage applied when an underlying layer located under acoil layer is to be removed. A conventional method has carried oution-milling under an acceleration voltage larger than 500 V because alarger acceleration voltage can shorten a time for completing themethod. However the inventor has found that with the increase of anion-milling acceleration voltage, a carbonyl peak intensity ratio isalso increased with the result of the deterioration of electricalinsulation of photoresist. Though FIG. 4 shows a relationship between anion-milling acceleration voltage and only a carbonyl peak intensityratio, the inventor has found that, taking an amount of otherhydrophilic groups present in a hard-cured photoresist, if a peakintensity ratio of all hydrophilic groups present in a hard-curedphotoresist layer is approximately 0.5, an ion-milling accelerationvoltage equal to or smaller than 500 V can provide a thin film headhaving no problems. A smaller amount of hydrophilic groups is morepreferable. Hence, it is preferable to carry out ion-milling at anacceleration voltage equal to approximately 400 V.

The invention provides the following advantages. The inventiondeteriorates the hydrophilic property of the hard-cured photoresistlayer at a surface thereof to thereby enhance a cross-linking density ofa hard-cured photoresist layer. This enhances the electrical insulationand reduces noises of a thin film recording head. A yield of a thin filmrecording head is also enhanced.

In addition, the fluctuations of internal stress of a hard-curedphotoresist layer are decreased by adsorbing humidity thereinto tothereby make it easy to control magnetic domain of a permalloy layergrowing adjacent to the photoresist layer.

The above and other objects and advantageous features of the presentinvention will be made apparent from the following description made withreference to the accompanying drawings, in which like referencecharacters designate the same or similar parts throughout the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view illustrating a prior thin filmrecording head.

FIG. 2 is a graph showing a relationship between a leak current and acarbonyl peak intensity ratio.

FIGS. 3A, 3B, 3C and 3D are cross-sectional views illustrating steps ofa method for manufacturing a thin film recording head in accordance withthe invention.

FIG. 4 is a graph showing a relationship between an ion-millingacceleration voltage and a carbonyl peak intensity ratio.

FIGS. 5A, 5B, 5C and 5D are cross-sectional views illustrating steps ofa method for manufacturing a thin film recording head in accordance withthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments in accordance with the present invention will beexplained hereinbelow with reference to drawings.

Embodiment 1

With reference to FIGS. 3A to 3D, hereinbelow will be explained stepsfor manufacturing a thin film magnetic head as well as a structure ofthe thin film magnetic head. As illustrated in FIG. 3A, first, on an Al₂O₃ -TiC substrate 1 is formed an insulative layer 2 composed of aluminaby means of sputtering. Then, on the insulative layer 2 is formed alower magnetic layer 3 having a thickness of 3 μm by sputtering orplating soft magnetic substance such as a permalloy. On the lower polelayer 3 is then formed an insulative gap layer 4 composed of alumina andhaving a predetermined thickness. Then, an unnecessary rear portion ofthe insulative gap layer 4 is removed by etching. Then, photoresist isapplied on the insulative gap layer 4 by a spin-coating process in orderto eliminate an irregularity of the lower magnetic layer 3. Then, aresultant is subject to heat treatment at approximately 250 degreescentigrade to thereby form a hard-cured photoresist layer 5.

Then, as illustrated in FIG. 3B, on the hard-cured photoresist layer 5is formed a Cr layer 10 having a thickness of 0.1 μm which is to act asa layer for preventing the photoresist layer 5 from peeling off, and onthe Cr layer 10 is formed a Cu layer 11 having a thickness of 0.1 μmwhich is to act as a underlying layer for plating. The Cr and Cu layers10, 11 are formed by means of sputtering. Then, a coil layer ispatterned on the Cu layer 11 with photoresist to thereby form coils 6 byplating. Then, the photoresist having been used for coil patterning isremoved, and further, as illustrated in FIG. 3C, an unnecessary portionsof the Cu and Cr layers 10, 11 are removed by ion-milling. Anion-milling etching is carried out with ion-milling acceleration voltagebeing equal to or less than 400 V. As a result, a surface portion of thehard-cured photoresist layer 5, namely a portion located lower than thecoils 6 and between the coils 6 turns into a low-hydrophilic layer 16.

Then, as illustrated in FIG. 3D, in order to smooth irregularitiesformed by the coils 6, photoresist is applied over the coils 6, and thensubject to a heat treatment at 250 degrees centigrade. Thus, there isformed a hard-cured photoresist layer 15. Then, on the insulativehard-cured photoresist layer 15 is formed an upper magnetic layer in asimilar way as that of the lower magnetic layer 3 in the case of onecoil layer structure, or a coil pattern is formed again in the casemultiple coil layers structure. Thus, a transducer portion of a thinfilm recording head is completed.

The thus obtained thin film recording head has a peak intensity ratio ofa hydrophilic group of 0.35, and also has a superior leak currentcharacteristic wherein a leak current is about 10⁸ A.

Embodiment 2

FIGS. 5A to 5D shows another embodiment for manufacturing a thin filmrecording head in accordance with the invention. As illustrated in FIG.5A, first, on an Al₂ O₃ -TiC substrate 1 is formed an insulative layer 2composed of alumina by means of sputtering. Then, on the insulativelayer 2 is formed a lower magnetic layer 3 having a thickness of 3 μm bysputtering or plating soft magnetic substance such as a permalloy. Onthe lower pole layer 3 is then formed an insulative gap layer 4 composedof alumina and having a predetermined thickness. Then, an unnecessaryrear portion of the insulative gap layer 4 is removed by etching. Then,photoresist having a thickness of 5 μm is applied on the insulative gaplayer 4 by a spin-coating process in order to eliminate an irregularityof the lower magnetic layer 3. Then, a resultant is subject to heattreatment at approximately 250 degrees centigrade to thereby form ahard-cured photoresist layer 5. Then, into a surface of the hard-curedphotoresist layer 5 is implanted ion of an impurity at an amount ofdopant in the range of 10¹⁴ to 10¹⁵ /cm⁻² in order to avoid qualitychange of the hard-cured photoresist layer 5. The impurities areselected from impurities having a small diffusion coefficient in ahard-cured photoresist. Such impurities include P, As, B, Si and Sn.

Then, as illustrated in FIG. 5B, on the hard-cured photoresist layer 5is formed a Cr layer 10 having a thickness of 0.1 μm which is to act asa layer for preventing the photoresist layer 5 from peeling off, and onthe Cr layer 10 is formed a Cu layer 11 having a thickness of 0.1 μmwhich is to act as a underlying layer for plating. The Cr and Cu layers10, 11 are formed by means of sputtering. Then, a coil layer ispatterned on the Cu layer 11 with photoresist to thereby form coils 6 byplating. Then, the photoresist having been used for coil patterning isremoved, and further, as illustrated in FIG. 5C, an unnecessary portionsof the Cu and Cr layers 10, 11 are removed by ion-milling. It is notnecessary to set the ion-milling acceleration voltage to be under 500 V.Then, as illustrated in FIG. 5D, in order to smooth irregularitiesformed by the coils 6, photoresist is applied over the coils 6, and thensubject to a heat treatment at 250 degrees centigrade and further to anion-implantation. Thus, there is formed a hard-cured photoresist layer15 having a thickness of 5 μm. The ion implantation increases across-linking density of the hard-cured photoresist layer, and henceincreases inter-molecular energy of the photoresist. Accordingly, thephotoresist layer remains unchanged even when it would be subject tosubsequent ion-milling. The ion implantation is carried out only whenmultiple coils are to be formed. When a single coil is to be formed, anupper magnetic layer is formed in place of the ion implantation in thesame way as that of the lower magnetic layer. Thus, a transducer portionof a thin film recording head is completed.

The ion-implanted hard-cured photoresist layer has a surface portionhaving a cross-linking density higher than that of a lower portionthereof by approximately 10% or more. The surface portion of theion-implanted hard-cured photoresist layer remains unchanged even whenthe surface portion is subject to subsequent ion-milling and moistureabsorption, and thus provides a superior electrical insulation property.

While the present invention has been described in connection withcertain preferred embodiments, it is to be understood that the subjectmatter encompassed by way of the present invention is not to be limitedto those specific embodiments. On the contrary, it is intended for thesubject matter of the invention to include all alternatives,modifications and equivalents as can be included within the spirit andscope of the following claims.

What is claimed is:
 1. A method for manufacturing a thin film recordinghead, comprising:forming a first hard-cured photoresist layer over alower magnetic substance; forming a metal underlying layer for platingover said first hard-cured photoresist layer; forming a coil layer onsaid metal underlying layer, said coil layer being configured in a coilpattern; removing unnecessary portions of said metal underlying layer toexpose a top surface of said first hard-cured photoresist layer byion-milling in Ar atmosphere with an acceleration voltage of ion-millingbeing equal to or less than 500 V thereby maintaining a hydrophiliccontent of said first hard-cured photoresist layer at a predeterminedlevel or less; forming a second hard-cured photoresist layer over saidcoil pattern: and forming an upper magnetic substance on said secondhard-cured photoresist layer.
 2. The method as recited in claim 1,wherein said metal underlying layer is composed of Cu.
 3. The method ofclaim 1, wherein said acceleration voltage of ion milling is less than400 V.
 4. The method of claim 3, further comprising forming ananti-peeling layer over said first hard-cured photoresist layer.
 5. Themethod of claim 1, wherein the predetermined level for the hydrophiliccontent comprises a peak intensity ratio of a hydrophilic group of 0.5or less.
 6. A method for manufacturing a thin film recording head,comprising:forming a first hard-cured photoresist layer over a lowermagnetic substance; forming an underlying layer for plating over saidfirst hard-cured photoresist layer; forming a coil layer on saidunderlying layer, said coil layer being configured in a coil pattern;forming a second hard-cured photoresist layer over said coil pattern;forming an upper magnetic substance on said second hard-curedphotoresist layer; and implanting ion of an impurity at an amount ofdopant in the range of 10¹⁴ to 10¹⁵ cm⁻² into a portion of said secondhard-cured photoresist layer located lower than said coil layer andbetween coils comprising said coil pattern to decrease a leakage currentin said second hard-cured photoresist layer.
 7. The method as recited inclaim 6, wherein said impurity is selected from impurities that resistdiffusion in a thermosetting photoresist.
 8. The method as recited inclaim 7, wherein said impurities include P, As, B, Si and Sn.
 9. Themethod of claim 6, further comprising implanting ion of an impurity atan amount of dopant in the range of 10¹⁴ to 10¹⁵ cm⁻² into a top portionof said first hard-cured photoresist layer.
 10. The method of claim 9,further comprising forming an anti-peeling layer on said firsthard-cured photoresist layer.
 11. The method of claim 10, wherein afterforming the coil layer on said underlying layer, ion milling saidunderlying layer to a top surface of said first hard-cured photoresistlayer.
 12. The method of claim 9, wherein after ion implantation of theimpurity in the first hard-cured photoresist layer, the top portion ofsaid first hard-cured photoresist layer has a cross-linking density thatis at least 10% higher than a cross-linking density of a lower portionof said first hard-cured photoresist layer.